On a soggy morning this past April, Daniel Rosenfeld moved briskly
through an overcast parking lot into one of many monolithic brick
structures that dot NASAs Goddard Space Flight Center. When he
arrived at the conference room, he switched on a laptop and began
bringing up satellite images of what looked like an apocalyptic vision
of the East Coast. From Massachusetts to North Carolina, swirling red,
orange and yellow clouds floated above a blue landscape.

Peering over his glasses and intently at the screen, he pointed to an especially fiery spot on the map
near the border of Pennsylvania and New Jersey. "The atmosphere
here is fully polluted," he said. "Those colored streaks are
mostly due to man-made aerosols."

The dense concentration of
powerplants, factories, trucks, and automobiles on the U.S. east coast continuously emit soot and
other particulate pollutants into the sky. These small particles suspended in the airaerosolsoften
end up interacting with clouds, forming more, smaller droplets than those found in an unpolluted
cloud. In this satellite image the yellow clouds scattered over the northeast are polluted clouds with
small water droplets. The pink clouds over Canada have larger droplets, and are relatively clean. Because the aerosols
prevent cloud water droplets from growing large enough to precipitate, this type of
pollution can reduce rainfall. (Image by Daniel Rosenfeld, Hebrew University of Israel)

He went on to explain that aerosols in this instance have little to
do with household cleaning products. For atmospheric scientists such as
him, aerosols are defined as any microscopic particle suspended in the
atmosphere. Not only do they make our sunsets particularly vivid and our
air particularly gritty on a hot summers day, but they also create
clouds in the sky. While most atmospheric aerosols originate from
natural sources such as the sea spray and volcanoes, he said nearly all
the color enhanced yellow and orange clouds in his image have been
affected by aerosols created by factories, power plants and cars up and
down the East Coast.

For the past six years, Rosenfeld and a team of scientists from the
Hebrew University of Israel used NASA satellites and remote sensing
techniques to track how man-made aerosols change clouds. They recently
discovered that aerosol particles from factories and power plants
increase the number of droplets in clouds they pollute. In doing so, the
pollutants create brighter clouds that retain their water and do not
produce rain. These results put to rest a decades-long debate about
human-generated pollutants and biomass burning as well as verify that
our manufacturing processes and our need for energy are changing the
global climate and local weather systems.